The present invention relates to a reinforcing textile thread for an inflatable sail, such as a rigging sail or a flight sail. It also relates to a rigging sail, in particular a mainsail, including at least one reinforcing textile thread.
On a sailboat, the mainsail is generally the lowest sail of the mainmast, and the most expansive when it is fully deployed. For some time, this sail was made from a taffeta weave from polyester threads. Recently, in particular in the field of competition rigging equipment, it has been proposed to replace the taffeta weave with lighter complexes that are stronger and transmit the propulsion forces from the wind more effectively. These complexes typically assume the form of a member including two films of a plastic material, which are glued to each other, trapping a reinforcing grid between them. This grid is formed by a set of threads, arranged in a regular pattern, such as a diamond or a square, which, by repetition, defines the entire grid. This means that the grid is a two-dimensional assembly of threads, often a weave, with which a main rectilinear direction and another rectilinear direction, for example perpendicular to the preceding, can be associated, both belonging to the plane of the grid. This structure gives the grid tear strength and, more generally, an ability to mechanically strengthen the two side-by-side films of the complex, with properties that are not generally identical in all directions of the plane, but which are pre-established relative to the aforementioned main direction, based on the pattern of the grid.
Inasmuch as within a sail, in particular a mainsail, service constraints are established based on curved lines of action, which generally connect the apices and/or edges of the sail in pairs, the aforementioned grid is biased, within the complex, in changing directions relative to the main direction of the grid, with local risks of damaging the complex. To strengthen the complex, it is known to add, inserted between the two films, multiple individual reinforcing threads, which are respectively oriented within the complex along predetermined lines of action such that, during use, the strains undergone by the sail are essentially or almost exclusively borne by those reinforcing threads, which are dimensioned accordingly to sustain the mechanical strength of the sail, while the other layers making up the sail, i.e., the two films and the grid, may then be dimensioned minimally in terms of mechanical strength: the overall weight of the sail is decreased as a result. In practice, the individual reinforcing threads generally used are made from aramid, carbon or polyester.
That being said, the use of these individual reinforcing threads causes practical problems. Given their non-negligible thickness relative to the thicknesses of the other components of the complex, these threads create significant relief discontinuities: in the long-term, these discontinuities are the beginning of delamination of the complex, as well as areas of wear of the complex due to friction with the wind. These drawbacks are even more pronounced in the apices of the sail, where the end parts of a large number of these threads are concentrated and superimposed on each other, if applicable while allowing free spaces to remain between them, not occupied by the films or by the glue of the complex. The lifespan of the sail is then limited as a result.
Similar technical considerations exist for rigging sails other than the mainsail, or even for other types of sails inflatable by the wind, such as flight sails, which are, inter alia, kite surf sails, paragliding sails, etc., when efforts are made to reinforce such inflatable sails using directed reinforcing individual threads.
To avoid the aforementioned drawbacks relative to individual reinforcing threads, WO-A-94/11185 proposed to replace those individual threads with bands each made up of multiple parallel monofilaments, which, in the matrix binding them to each other, are arranged in a single layer, the thickness of which is equal to the diameter, typically smaller than 20 μm, of the monofilaments. The sail obtained thus includes several of these bands such that the monofilaments of each of them extend in respective directions that are inclined relative to one another: within the complex making up this sail, the interlacing monofilament density is increased as a result. This solution is attractive on paper, but is particularly difficult to implement, as it requires manufacturing, in particular by pultrusion, the bands described above, having a thickness of a single monofilament. Furthermore, this solution requires that each of the bands occupies the entire expanse of the complex, thereby representing part of the total thickness of the complex, the flexibility of which is deteriorated as a result: consequently, it is necessary to provide as many bands as there are directions of lines of action to be reinforced, without, furthermore, being able to reinforce a line of action with a curved profile continuously.
Furthermore, in a field remote from inflatable sails, EP-A-0,625,417 discloses a reinforcing thread that includes a sheath, inside which filaments run in a powder. The aerated structure of this powder is used to impart considerable flexibility to the thread. In practice, this reinforcing thread cannot be used within a complex with laminated outer films.
The aim of the present invention is to propose individual reinforcing threads which, while guaranteeing an effective directed reinforcing effect for an inflatable sail, does not limit the lifespan thereof, in particular without causing premature wear thereof.